The present invention relates to polyols which can be obtained by a simple process. As used herein, unless explicitly specified, the term polyols is to be understood as meaning both polyether polyols and polyether ester polyols. The present invention also provides a simple process for the production of these polyols, and also the production of polyurethane materials from the reaction of these polyols with a polyisocyanate component.
Polyols that are suitable for the production of polyurethane materials such as flexible or rigid foams and compact materials such as elastomers, are generally obtained by polymerisation of suitable alkylene oxides onto polyfunctional starter compounds, i.e. starter compounds containing a plurality of Zerewitinoff-active hydrogen atoms. A very wide variety of processes, some of which complement each other, have for a long time been known for carrying out these polymerisation reactions.
On the one hand, the base-catalysed addition of alkylene oxides to starter compounds having Zerewitinoff-active hydrogen atoms is of importance on a commercial scale. on the other hand, the use of double metal cyanide compounds (“DMC catalysts”) for carrying out this reaction is becoming increasingly important. The use of highly active DMC catalysts, which are described, for example, in U.S. Pat. No. 5,470,813, EP-A 700 949, EP-A 743 093, EP-A 761 708, WO 97/40086, WO 98/16310 and WO 00/47649, allows polyether polyols to be prepared with very low catalyst concentrations (25 ppm or less), so that it is no longer necessary to separate the catalyst from the finished product. However, these catalysts are not suitable for the preparation of short-chained polyols or of polyols having high ethylene oxide contents. The basic catalysts which have been known for a long time, for example those catalysts based on alkali metal hydroxides, allow short-chained polyols and/or polyols having a high ethylene oxide content to be prepared without problems, but the catalyst generally has to be removed from the crude alkaline polymer by means of a separate working-up step. The (Lewis) acid-catalysed addition of alkylene oxides to suitable starter compounds is of lesser importance.
The base-catalysed addition of alkylene oxides such as, for example, ethylene oxide or propylene oxide, to starter compounds having Zerewitinoff-active hydrogen atoms is typically carried out, as already mentioned, in the presence of alkali metal hydroxides. It is also possible, however, to use alkali metal hydrides, alkali metal carboxylates, alkaline earth hydroxides or amines such as, for example, N,N-dimethylbenzylamine or imidazole or imidazole derivatives as catalysts in this process.
After the addition of the alkylene oxides, the polymerisation-active centers on the polyether chains must be deactivated. Various procedures are possible for achieving this. For example, neutralization can be carried out with dilute mineral acids such as sulfuric acid or phosphoric acid. The strength of the second dissociation stage of sulfuric acid is sufficient for the protonation of the alkali metal hydroxides formed by hydrolysis of the active alcoholate groups, so that 2 mol of alcoholate groups can be neutralized per mol of sulfuric acid used. Phosphoric acid, on the other hand, must be used in an equimolar amount relative to the amount of alcoholate groups to be neutralized. In both cases, the salts formed in the neutralization and/or during the removal of the water by distillation must be separated off by means of filtration processes. Distillation and filtration processes are time- and energy-intensive and, in addition, are not readily reproducible in some cases. Many processes have therefore been developed which can be carried out without a filtration step and, in many cases, also without a distillation step: Neutralization with hydroxycarboxylic acids such as, for example, lactic acid is described in WO 9820061 and U.S. Published Patent Application 2004167316 for the working-up of short-chained polyols for rigid foam applications; such processes are widespread and well established. U.S. Pat. No. 4,521,548 describes how the polymerisation-active centers can be deactivated in a similar manner by reaction with formic acid. The metal carboxylates formed after neutralization with hydroxycarboxylic acids or formic acid dissolve in the polyether polyols to give a clear solution. However, a disadvantage of these processes is the catalytic activity of the salts that remain in the products, which is undesirable for many polyurethane applications. Therefore, in JP-A 10-30023 and U.S. Pat. No. 4,110,268, aromatic sulfonic acids or organic sulfonic acids are used for the neutralization; these likewise form salts which are soluble in the polyether polyols but are less basic and are distinguished by lower catalytic activity. A crucial disadvantage here is the high cost of the sulfonic acids. Working up by means of acidic cation exchangers, as is described in DE-A 100 24 313, requires the use of solvents and the removal thereof by distillation, and is accordingly likewise associated with high costs. Phase separation processes require only a hydrolysis step and not a neutralization step and are described, for example, in WO 0114456, JP-A 6-157743, WO 9620972 and U.S. Pat. No. 3,823,145. The phase separation of the polyether polyols from the alkaline aqueous phase is assisted by the use of coalescers or centrifuges; here too, solvents must often be added in order to increase the difference in density between the polyether phase and the water phase. Such processes are not suitable for all polyether polyols; they are unsuccessful in particular in the case of short-chained polyether polyols or polyether polyols having high ethylene oxide contents. The working up of polyether ester polyols cannot be carried out by such phase separation processes because the long period of contact of the polyether ester chains with the alkaline aqueous phase would doubtless lead to irreversible hydrolysis of the ester bonds. The use of solvents is cost-intensive, and centrifuges require a high outlay in terms of maintenance.
In the case of amine-catalysed alkylene oxide addition reactions, further working up can be dispensed with provided that the presence of the amines in the polyols does not impair the production of polyurethane materials. Only polyols having comparatively low equivalent weights can be obtained by amine catalysis, see in this connection, for example, Ionescu et al. in “Advances in Urethane Science & Technology”, 1998, 14, p. 151-218.
Therefore, the object of the present invention was to find an inexpensive working-up process for ethylene-oxide-containing polyols prepared with alkali or alkaline earth hydroxide, carboxylate or hydride catalysis, in which the process does not exhibit the disadvantages of the processes of the prior art. In particular, the polyols are to have low base contents, which ensures that they are widely usable in both “one shot” and prepolymer applications.